About Us
The Discovery of Down Syndrome
Chromosomal Technology
The Name Debate
Types of Down Syndrome
About the Child with Down Syndrome
Education and Beyond
Other Chromosomal Disorders
About Us
In 1974, a group of concerned parents formed Down’s Children Inc., now the Down Syndrome Society of South Australia Inc. This group established a service to provide family support and specialist education programs.
Today through Government funding and considerable fundraising efforts, the Society is able to offer a range of services to people with Down syndrome and their families throughout South Australia. Some individuals are born with chromosomal disorders that result in similar characteristics to the child with Down syndrome. These individuals are eligible to access the Society’s services following a referral from a Geneticist or Paediatrician.
Down Syndrome - an overview
Down syndrome is a congenital chromosomal condition that occurs approximately once in every 600 – 700 live births in South Australia. The term ‘congenital’ means that the condition is present at birth; it is not something that develops or is ‘caught’ later on.
Down syndrome results in intellectual and physical delay/disability and is thought to occur more frequently than any other specific kind of intellectual disability. Incidences of Down syndrome have been found in every race and social class throughout history.
Whilst we don’t know why it happens we do know that there is nothing that can be done prior to or during a pregnancy to prevent it. At the present time the only known ‘risk’ factor is maternal age however it should be noted that approximately 80% of babies born with Down syndrome are born to mothers under the age of 30.
The links below will take you to the respective sections on this page or you can scroll through the entire commentary.
The Discovery of Down Syndrome
Characterised by a number of physical features, the syndrome was first described by Dr J. Langdon H Down (usually referred to in the literature as Dr Langdon Down) in 1866. Although this was the first official description, there is evidence to suggest it existed long before this.
Dr Down was an English physician and he spent many years working with children described at the time as being “gravely neglected” and “mentally retarded”. In trying to identify the different “types” of mental afflictions present in the children he saw, Dr Down grouped them by appearance and likened each group to a particular race. In more than 10% of the cases presented to him the child belonged to the group who most closely resembled the Mongolian race. Thus the terms ‘Mongol’, ‘Mongolism’ and ‘Mongoloid’ were often used to describe a person with this syndrome. Later it would become known as Down syndrome.
Dr Down - Ethnic Classification of Idiots - 1866 is a link to Dr Down’s paper – note that at the time the term ‘idiot’ was accepted medical terminology.
Chromosomal Technology
Whilst Dr Down had been able to identify characteristics and features peculiar to the disorder he was unable to say why this occurred. Over the next eight decades theories put forward to explain the cause of Down syndrome included yet to be identified inheritable factors and injuries sustained during birth. The only common element in the research was an apparent link between the prevalence of Down syndrome and increased maternal age but the cause still remained a mystery.
When karyotype technology was discovered in the 1950’s scientists were able to determine what a normal cell in the human body should look like. With this breakthrough came the revelation that Down syndrome was in fact caused by an error in cell development.
Chromosomes contain thousands of genes that carry the genetic code that controls and instructs cell division, growth and function. They are the structures inside the nucleus of living cells that contain the hereditary information that makes us all (with the exception of identical twins) unique. Every cell in the human body should contain 46 chromosomes, which exist in pairs (numbers 1-23) with one copy inherited from each parent.
In 1959 Professor Jerome Lejeune from France discovered that people with Down syndrome had 3 copies of chromosome number 21 instead of 2 and as a result the condition became scientifically known as Trisomy 21.
The Name Debate
In the early 1960’s a group of predominantly Asian geneticists got together to condemn the use of the term ‘Mongolian idiocy’ to describe the syndrome suggesting that it was embarrassing. Thankfully this was successful and today the inappropriate terms of ‘Mongol’, ‘Mongoloid’ and ‘Mongolism’ are rarely heard; instead replaced with the terminology ‘Down’s syndrome’. A push by the National Institutes of Health in the USA in the mid 1970’s lead to another revision and today the accepted professional term is Down syndrome and this is the terminology used throughout Australia. In the UK and parts of Europe ‘Down’s syndrome’ is still used.
The accepted scientific name remains Trisomy 21.
Types of Down syndrome
The human body is made up of a mass of cells – millions of cells to be exact – and it is the content of these cells that determine who we are. A chromosome is made up of many genes and in so called ‘normal’ humans, 23 pairs of chromosomes are present in every cell of the body. One set of 1-23 is inherited from each parent at the time of conception with the 23rd pair responsible for determining an individual’s sex.
In cases where there are more (or less) chromosomes than normal, a chromosomal abnormality of some sort is said to be present. It is impossible to count the number of chromosomal abnormalities possible. In some people there is no manifestation of the abnormality i.e., they not show any affects. These people are known as ‘carriers’ and whilst the abnormality poses no problem for them it can be a problem for their offspring. In other cases, such as Down syndrome, the abnormality almost always shows itself.
Chromosome 21 is the second smallest of all chromosomes (they have been labelled from 1 to 22 in descending order of size). Exactly how the 21st chromosome replicates itself will determine the type of Down syndrome a person has.
More detailed information about Genes, Chromosomes and Down syndrome can be found on the websites of The Centre for Genetics Education, Australia (and in particular their fact sheets on Genes and Chromosomes and Down syndrome) and Dr Len Leshin.
- Standard Trisomy 21
The events that cause Down syndrome occur before conception and lead to a fertilised egg with an abnormal number of chromosomes in each cell - 47 rather than the normal 46. This is called a meiotic nondisjunction event.
‘Meiosis’ is the technical term used to describe the cell division that occurs in the reproductive organs of men and women and when it happens correctly eggs and sperm should each carry a set of 23 chromosomes. This is called a disjunction. However in some cases a pair fails to separate which leads to the one gamete (i.e., either a sperm or egg cell) having 24 chromosomes and the other 23 chromosomes. This is called a nondisjunction. As a result when this gamete of 24 chromosomes merges with a normal gamete (23 chromosomes) the embryo will have 47 chromosomes, which includes 3 copies of chromosome 21.
This is known as Standard Trisomy 21 and occurs in approximately 95% of children with Down syndrome.
- Translocation Trisomy 21
Occasionally the extra copy of chromosome 21 is attached to another chromosome in the egg or sperm and this may result in Translocation Trisomy 21. This rearrangement of genetic material usually sees the extra copy of chromosome 21 attached to chromosome 14. Whilst the number of chromosomes present appears to be normal there is still a triplication of genetic material from chromosome 21 and hence Down syndrome results. The incidence of Translocation is 2-3% and without a karyotype test it is indistinguishable from standard trisomy 21.
Whilst Down syndrome is usually an unexpected event without a detectable cause, in 1 out of every 3 cases of Translocation it is possible that the condition was inherited from a parent. Some parents have what is called a ‘balanced translocation’ where the extra genetic material is attached to another chromosome but it does not affect their health. It is important for the parents to undergo a karyotype assessment to assess the risk for future pregnancies.
- Mosaic Trisomy 21
In Standard Trisomy 21 all cells in the body carry 47 chromosomes however in Mosaic Trisomy 21 there is a mixture of trisomic and non trisomic cells i.e., some cells have 47 chromosomes whilst others have the usual 46. This occurs in approximately 1-2% of cases.
There are 2 ways Mosaic Trisomy 21 can occur. One is that a nondisjunction event (refer to Standard Trisomy 21 above) occurs in the early stages of a normal embryo’s development that leads to a small number of cells carrying triplicate material. The other is that an embryo already carrying Down syndrome splits in nondisjunction and a proportion of the cells revert back to a ‘normal’ formation.
The ratio of normal to abnormal cells varies widely amongst individuals with Down syndrome and impacts on the extent to which Down syndrome is evident.
The Child with Down syndrome
Whilst children with Down syndrome may have similar physical characteristics, facial features and health issues it is important to remember that each is an individual whose physical, emotional and intellectual development is influenced by their unique genetic makeup. They will have a wide range of abilities which are determined by heredity and early upbringing.
Our genes are what make us individuals. However the excess (or over expression) of genetic material on the 21st chromosome will lead to people with Down syndrome sharing a number of common physical characteristics. Whilst there have been more than 50 physical characteristics found in individuals with Down syndrome doctors only need to see 6 or 7 before they suspect Down syndrome.
This list includes:
- Almond shaped eyes with an upward and outward slant
- Fold of skin (epicanthal fold) on the inner side of the eye
- Small white patches on the edge of the iris (Brushfield spots)
- A broad face that is flat in appearance
- Fontanelles are larger than normal and take longer to close due to slow growth
- A shorter neck which has loose folds of skin at the back and sides (this disappears with growth)
- Ears are smaller and lowset
- Limbs are short in relation to the body
- Broad, flat hands with short fingers
- Little finger slants inward
- A single ‘palmar’ crease across the hand instead of two
- Broad feet with short toes
- Larger space (or cleft) between the first and second toes
- Poor muscle tone (hypotonia)
- Loose jointedness (hyperflexibility)
A child with Down syndrome is generally delayed in reaching milestones such as sitting, crawling, walking, talking, toileting etc.
For most children with Down syndrome the future is brighter today than it might have been only a short while ago. Educational and medical techniques have made, and continue to make, great advances in helping children with Down syndrome lead a life of dignity, meaning and independence
For more information on the medical/health and behavioural issues related to Down syndrome please refer to our Medical/Health Issues and Behaviour pages.
Education and Beyond
Early Intervention Programs are particularly beneficial in early childhood. As for any child, frequent contact with other children from an early age is essential. Most children with Down syndrome benefit immensely from attending a child care centre and/or pre-school. Later, the majority attend their neighbourhood school with special education support with many now successfully learning how to read and write.
A wide range of vocational opportunities are now available and an emphasis is placed on the adolescent and adult developing independent living skills and being fully involved in a range of recreational and community activities.
For more information about the services offered by the Society to support people at school and beyond click on the relevant links.
Other Chromosomal Disorders
In addition to providing services to individuals with Down syndrome, the Society supports people with other similar chromosomal disorders. Generally speaking these other disorders occur less frequently than Down syndrome.
The educational approach of the Down syndrome society has resulted in an early intervention program, which focuses on enhancing physical, intellectual, sensory and social development in a bid to assist the individual realise their full potential.
In order to access the services offered by the Society a referral must be made through either a Paediatrician or a Geneticist.
Disorders such as Cri du Chat syndrome, Prader-Willi syndrome and Williams syndrome, for example, are known to have similar impacts to Down syndrome on a person’s intellectual and physical development and therefore the programs offered by the Society can have some benefit. A brief description of these disorders is provided here with links provided to more detailed information.
- Cri du chat
One of the earliest indications that a baby may have Cri du chat syndrome is the presence of a high-pitched, monotone cry and it is after this characteristic that the syndrome was first named; “Cri du chat” is French for “cat’s cry”.
This syndrome, believed to occur in 1:25,000 to 1:50,000 births, is a genetic disorder caused by a missing or deleted part of chromosome number 5. The size and location of the missing (or deleted) part of the chromosome determines the degree to which the child will be affected. Although the affect on individuals varies greatly, it is anticipated that all babies with Cri du chat will experience degrees of intellectual disability, speech/language delay and delays in the development of motor skills. The presence of additional health issues will depend on how severely the child is affected.
For more detailed information on Cri du chat syndrome refer to the Cri du chat support group of Australia.
- Prader-Willi Syndrome
Prader-Willi syndrome (PWS) is estimated to affect 1 in 15,000 people and is a complex genetic disorder. Abnormalities within the genes of chromosome 15 results in PWS and in almost all cases, these genetic errors are spontaneous not hereditary.
The syndrome is characterised by two distinct (and almost contradictory) stages. The first begins at birth with the baby having very low tone, which leads to significant feeding problems. Often the baby will be described as failing to thrive. The onset of stage 2 sees the child develop an insatiable appetite and an ongoing battle with weight begins. There is no way to predict exactly when stage 2 will begin but in most cases the transition can be seen to occur somewhere between the ages of 2 and 4. In addition, a person with PWS will experience learning difficulties and have poor social and emotional skills.
For more detailed information on Prader-Willi syndrome please refer to the Australian Prader-Willi Syndrome (PWS) Site
- Williams Syndrome
Occurring at a rate of 1 every 20,000 births, Williams syndrome, or Williams-Beuren syndrome as it is sometimes referred, is a rare genetic condition resulting from genetic imperfections associated with chromosome number 7. People with Williams syndrome share similar facial characteristics and experience varying degrees of physical and developmental disabilities.
Although present from birth, it is common for a diagnosis of Williams syndrome to be made at a later date.
